A capacitive sensor array with a sensor electrode with whose aid the approach of an object is to be detected, and with a control and evaluation circuit that is linked to the sensor electrode and detects a capacity change of the sensor electrode as compared to mass by periodically linking the sensor electrode with an operating voltage at a predetermined frequency and evaluating at least one parameter of a current or voltage progression that is dependent on the periodic charging and discharging of the sensor electrode in order to detect the capacity change is, for example, known in the U.S. Pat. No. 5,730,165 as well as the corresponding patent document DE 196 81 725 B4. The parameter of a current or voltage progression that is dependent on the periodic charging and discharging of the sensor electrode herein consists of a voltage that can be measured over a condenser and depends on a charge that is accumulated in the condenser, wherein this charge is accumulated by periodically charging the sensor electrode by linking it to the operating voltage and subsequently discharging it again by connecting it to the condenser. Another such capacitive sensor is known from the patent document EP 1 339 025 B1.
A capacitive sensor array with a sensor electrode, with a mass background electrode that is mounted with a gap behind the sensor electrode, and with a shielding electrode that is arrayed between the sensor electrode and the mass background electrode and is linked to the sensor electrode via a control and evaluation circuit in such a manner that its potential follows the potential of the sensor electrode is, for example, known from the publications EP 0 518 836 A1, U.S. Pat. No. 6,825,752 B2, DE 101 31 243 C1 and DE 10 2006 044 778 A1. The provision of an shielding electrode between the sensor electrode and the background electrode that is on mass potential as known from these printed documents has the advantage that the sensitivity of the capacitive sensor that is formed in this manner towards changes in the space ahead of the sensor electrode, e.g. by the introduction of objects, is heightened. This is particularly due to the fact that the field which spreads out from the sensor electrode ranges more strongly into the space ahead of the sensor electrode (detection range) because a large part of the field is no longer short circuited to the background electrode that is connected to mass potential, as would be the case if there were no shielding electrode. Due to the circumstance that the shielding electrode is connected to the sensor electrode in such a manner that it follows its potential, a strong electrical field is formed between the shielding electrode and the background electrode; specifically, however, practically no field is formed between the sensor electrode and the shielding electrode whose potential follows.
The known arrangement of a sensor electrode, shielding electrode and background electrode is commonly surrounded with an electrical insulator, such as a plastic layer, so that an insulating layer, such as a plastic layer, is present on the sensor electrode and therefore between the sensor electrode and the space to be monitored ahead of the sensor electrode, namely the detection zone. It has been shown that when such a capacitive sensor array is used in an environment that is burdened with dirt and humidity, e.g. on the exterior of a motor vehicle (e.g. as a proximity sensor in an exterior door handle), undesired capacity changes may occur due to contamination with water or humidity on the outer surface of the plastic coating of the sensor array; in the worst case, this may cause the sensor array to wrongly determine that an object has entered the detection zone in the space ahead of the sensor electrode.